The invention relates to a method and apparatus for applying molten size to a plurality of textile yarns.
Textile warp size is typically a polymeric material which is applied to individual textile yarns, whether filament or spun, to protect them from the physical abuse of the weaving operation. Although size could be applied to filling yarns, in practice the sizing of yarns for weaving is reserved exclusively for the treatment of warp yarns.
Commercial warp sizing machines, commonly known as slashers, in use today apply size to sheets of individual warp yarns in the form of aqueous solutions or suspensions. Aqueous slashing has other faults, but one of the most important and costly is the necessity to dry the sized yarns before they are wound up, i.e., beamed. With energy sources steadily rising in cost, drying of yarns is becoming a more and more expensive operation. The result is that means for supplanting aqueous slashing have for some time been sought in the trade.
During more than thirty years, repeated efforts have been made to develop sizes and means for applying them to yarn which would make the hot melt sizing of warp yarns commercially feasible. In Europe melt sizing is known as dry, i.e., solvent-free, sizing. Begun before 1950, developments originating with A. Hettwer in Austria culminated in the exhibition by the Swiss firm of Maschinenfabrik Ruti AG of a commercial dry sizing machine at the 1959 ITMA textile show in Milan. Sketchy information available today on the Ruti machine indicates that it featured a compressed-air size-doctoring device detailed in British Pat. No. 814,769 and elsewhere. No machine of this period seems to have been accepted by the trade, and the Ruti machine evidently had disappeared from the commercial scene by about 1962.
Shortly after Hettwer, in Swiss Pat. No. 308,545 (filed 1951), the German firm of Gebruder Sucker GmbH described an elaborate machine which evidently was intended for dry sizing of spun yarns. We have found no evidence that a size suitable for the machine was ever developed, or that the machine survived the fifties, if indeed it was ever commercialized.
Issued in 1969, U.S. Pat. No. 3,466,717 of Kuroda described a Japanese method and apparatus for the hot melt sizing of warp yarns with "a quickly solidifying size in which wax predominates". As with the Hettwer-Ruti machine before it, the Kuroda machine transferred molten size upward from a pool of size by means of one or more rollers to a sheet of warp yarns which picked up size from an upper roller surface as the roller turned. An emphasized feature of the Kuroda machine was a plurality of downstream smoothing, leveling or the like heated rollers, enclosed with the applicator roll within a preferably heated chamber, to provide even distribution of the size on the yarn before it passed to a cooling and solidifying zone. We are aware of efforts to commercialize this Japanese machine in the early seventies, but have heard nothing further of it in almost a decade.
Roughly coincident with the work in Japan, research on dry sizing methods and size compositions was going on in research institutes in eastern European countries, especially in East Germany and Poland. A section on "dry sizing" (pages 52-54) in a review article by Sontag (Deutsche Textiltechnik, 18, No. 1/2, 47-57 (1968)) briefly discussed work and problems to that time and introduced a laboratory dry sizing apparatus used at the Research Institute for Textile Technology, Karl-Marx-Stadt, East Germany. Difficulties encountered with sizing of spun (cotton) yarns are mentioned, but there is no indication that the problems were solved. This machine evidently was never commercialized. A later paper by Zawadzki ("Dry Sizing of Warps", Textiltechnik, 23, No. 7, 415-7 (1973)) described work on dry sizing at the Textile Research Institute in Lodz, Poland. A general discussion of the development of an industrial dry sizing machine and a diagrammatic sketch of the machine are given together with a statement that such a dry sizing machine had been installed in a filament weaving mill in Gorzow, Poland. We know of no further commercial developments along this line in the succeeding decade, however.
Careful study of the publications on these earlier melt, or dry, sizing systems shows that they achieved their only successes, however limited even they may have been, with filament yarns. With the exception of the Sucker patent, which directed attention principally to the dry sizing of spun yarns, all speak of spun yarn sizing only in terms of problems to be solved in the future. It is noteworthy that we have found no evidence of the further development or commercialization of the Sucker machine. Apparently, even in its own day it fell behind the Hettwer-Ruti machine, which was itself abandoned in the early sixties. In fact, apart from the following patent, and others utilizing its method and apparatus, we have found no evidence whatever of the commercialization of melt sizing of spun yarns, and no proof that the warp sizing of even filament yarns with melt sizes is being practiced commercially anywhere today.
In U.S. Pat. No. Re. 29,287, commonly assigned with the present application, a process and apparatus are described whereby molten size is applied to moving yarns as they pass tangentially through deep circumferential grooves in a heated rotating cylinder. After application the size solidifies almost instantly, without further manipulation in the molten state being either necessary or desirable. Although the process and apparatus of this patent may also be used to apply more thermally stable melt size compositions to yarn, a preferred embodiment is directed to applying sizes which, because of a tendency to thermal degradation, do not permit more than brief retention in the molten state. While not restricted to treatment of these yarns alone, the process and apparatus of this patent are concerned principally with the sizing of hairy spun yarns.
Inasmuch as most of the Swiss, Japanese, Polish, and German art references cited above are outwardly concerned only with problems seen in the melt sizing of filament yarns, they neither detail nor solve any problems which might have arisen with spun (staple) yarns. One of the most serious of such problems, in our experience, stems from the accumulation of fibrils, lint, and any other incidental debris, coming from either the yarn or from any other source, such as lint or dust in the atmosphere. (The Zawadzki reference above mentions such an atmospheric dust problem.) When such debris accumulates in the molten size it leads to nep-like lumps on the surface of the sized yarn, and subsequently to excessive yarn breaks in weaving.
Most prior art apparatus and methods for applying melt (or dry) size have been employed with various thermally stable waxes or waxy polymers such as polyoxyethylene glycol. As such they could afford not to be concerned with thermal degradation of the size while in the molten state. On the other hand the apparatus and method of U.S. Pat. No. Re. 29,287 had an additional capacity for sizing with compositions whose limited thermal stability did not permit long retention in the melt state.
The present invention provides advances in the method and apparatus of U.S. Pat. No. Re. 29,287. In particular it takes advantages of the concurrent development of melt size compositions having enhanced thermal stability.